Methods, respectively devices, of this type are known. They are methods which are carried out by means of pneumatics according to the principle of impact pressure. An example for that is presented in FIG. 3. For that purpose in the machine tool a pneumatic duct system which can be pressurized is installed at the support spots, respectively rest spots. This pneumatic system has to be installed in addition to the, if necessary, present, coolant/lubricant duct systems. In the duct system a constant supply pressure is generated. This is done, for example, by means of a pressure control valve. A downstream orifice or choke generates a pressure drop in the duct system. The pressure is measured between orifice or choke, and the measuring surface where air outlet openings are provided through which the air can escape, if no work piece, tool, or the like is positioned there. The pressure between the orifice or choke, and the measuring surface, respectively measuring point, depends on the relation between the orifice or adjustment of the choke, and air gap between the support spots of the work pieces, respectively the rest pieces. The change of pressure resulting from that is collected electrically either directly or indirectly over a pneumatic limit value switch, and processed in the machine control. Depending on the volume of the duct and the required accuracy the indexing time changes.
As the support points, respectively rest points, for the work piece have to be clean all the time it is necessary to clean the rest surfaces continuously from chips which might be there. For that purpose additionally coolant or blast air is used. Therefore the duct system has always to be pressurized in order to prevent also the liquid from penetrating the measuring channels. The secure recognition of the support of an object on the support surface could reasonably, according to the required accuracy, only be realized with pneumatic duct systems which had to be provided, as already mentioned, additionally in support surfaces.
Because of the variable supply pressure in the systems working with the coolant/lubricant, the required accuracy could not be reached in the same way as it could be reached in pneumatically charged systems. In this respect there are no hydraulic systems for support control according to the prior art which work with sufficient accuracy and reliability.
In the prior art there is also a device for pneumatic position control known where, via a pneumatic duct system, the pressure is measured on a choke device in flow direction before and after this choke, and a difference pressure sensor collects the respective differential pressure. However, this is also a support control system already described before, which is equipped for measuring, respectively the support control itself, with an additional pneumatic duct system, and thus becomes very expensive.
Another pneumatic support control installation with a differential pressure sensor is known. This also works by means of a differential pressure, and the evaluation via a differential pressure sensor. For this pneumatic support control system also an additional pneumatic duct system is necessary in addition to the coolant, respectively flushing agent, system of the machine tool.
Another support control system is known from the state of the art which already works with a liquid medium. Here, however, the position of the work piece on a reference surface is determined by a position detector. It determines the position of the work piece because of the counterpressure and the distance. The production of this measurement is also extremely complicated. Additionally the detectors are quite prone to malfunctions because of the effects of humidity.